1. Field of Invention
The present invention relates to a high performance telecommunications cable. In particular, the present invention relates to a cable designs designed to reduce PSANEXT.
2. Discussion of Related Art
The introduction of a new IEEE proposal for 10 G (Gigabit per second) transmission speeds over copper cable has spearheaded the development of new copper Unshielded Twisted Pair (UTP) cable designs capable to perform at this speed.
As known in the art, such UTP cables typically consist of four twisted pairs of conductors each having a different twist lay. Additionally, in many installations, a number of UTP cables are arranged in cable runs such that they run side by side and generally in parallel. In particular, in order to simplify the installation of UTP cables in cable runs, EMC conduit, patch bays or the like, a number of UTP cables are often bound together using ribbon, twist ties, tape or the like. A major technical difficulty in such installations is the electromagnetic interference between the twisted pair conductors of a “victim” cable and the twisted pair conductors of other cables in the vicinity of the victim cable (the “offending” cables). This electromagnetic interference is enhanced by the fact that, in 10 G systems where all twisted pairs of the UTP cable are required to support the high speed transmission, all conductors in a first cable are the “victims” of the twisted pair conductors of all other cables surrounding that first cable. These like pairs, having the same twisting lay, act as inductive coils that generate electromagnetic interference into the conductors of the victim cable. The electromagnetic interference, or noise, generated by each of the offending cables into the victim cable is generally known in the art as Alien Cross Talk or ANEXT. The calculated overall effect of the ANEXT into the victim cable is the Power Sum ANEXT or PSANEXT.
ANEXT and PSANEXT are important parameters to minimize as active devices such as network cards are unable to compensate for noise external to the UTP cable to which it is connected. More particularly, active systems at receiving and emitting ends of 10 G Local Area Networks are able to cancel internal Cross Talk (or NEXT) but cannot do the same with ANEXT. This is also due to some degree in the relatively high number of calculations involved if it is wished to compensate for ANEXT (up to 24 emitting pairs in ANEXT calculations vs. 3 emitting pairs in NEXT calculations).
In order to reduce the PSANEXT to the required IEEE draft specification requirement of 60 dB at 100 MHz, cable designers typically manipulate a few basic parameters that play a leading role in the generation of electromagnetic interference between cables. The most common of these are:
Geometry: (1) The distance between pairs, longitudinally, in adjacent cables; (2) the axial X-Y asymmetry of the pairs a cable cross-section; and (3) the thickness of the jacket; and
Balance: improved balance of the twisted pairs and of the overall cable is known to reduce emission of electromagnetic interference and increase a cable's immunity to electromagnetic interference.
Currently, the only commercial design of a 10 G cable incorporates a special cross web or spline which ensures that the twisted pairs of conductors are arranged off centre within the cable jacket. Additionally, this prior art cable incorporates twisted pairs with very short twisting lays and stranding lays that are known to enhance the balance of the twisting lays.